A MOS transistor is a basic configuration unit of an integrated circuit (LSI) included in a semiconductor device, and one of the most important aspects of performance of the MOS transistor is reliability of its gate insulating film. Reliability of the gate insulating film is known to depend on concentration of hydrogen included in the gate insulating film. For example, in a semiconductor device like a NAND type flash memory, it is usual for a passivation film configured from a silicon nitride film to be provided in a layer above a memory structure. This silicon nitride film contains a lot of hydrogen. Problems sometimes occur when this hydrogen is diffused to the gate insulating film. One such problem is that reliability of the gate insulating film degrades and a threshold voltage of the transistor fluctuates.
Accordingly, there has been proposed a method of manufacturing a semiconductor device in which a hydrogen block layer which is for avoiding diffusion of hydrogen and avoiding mixing of hydrogen in the gate insulating film, is provided temporarily midway through a manufacturing process. However, the hydrogen block layer of this conventional technology is provided only during the manufacturing process and is removed by etching in a final product, and is formed with a large film thickness of as much as 800 nm. Moreover, because the hydrogen block layer ends up being removed in the final product, it cannot suppress diffusion of hydrogen after shipment.